1. Field of the Invention
This invention relates generally to integrated circuits and monolithic electro-optical devices and, more particularly, to the fabrication of via holes.
2. Discussion of the Related Art
The fabrication of integrated circuit devices (ICDs) and monolithic electro-optical devices (MEODs) relies heavily on dry etching to produce structural features. One structural feature produced by dry etching is the via hole. Production of a via hole is the starting point for making an electrical contact to a buried metallization layer.
Dry etch processes leave residues in via holes, because energetic etchant ions sputter up atoms from underlying layers. If the dry etch stops on an underlying metallization layer, the ions of the etchant will sputter up metal particles, and the metal particles can then produce a metal veil along the walls of the produced via hole. Such a metal veil can impede subsequent formation of a high quality electrical contact in the via hole. In particular, collapse of the metal veil can partially block the via hole. This collapse causes an unpredictable contact resistance between a metal plug, which is subsequently formed in the via hole, and the underlying metallization layer. Since metal veils interfere with producing the types of high quality electrical contacts that are needed in ICDs and MEODs, it is desirable to eliminate such metal veils. While a careful selection of operating parameters of dry etches enables one to reduce metal veil formation, parameter selections do not completely eliminate veil formation. For that reason, it is desirable to have methods for cleaning metal veils from via holes.
Various embodiments provide methods for cleaning metal veils from via holes that are produced when a dry etch stops on a metal layer. Though these cleaning methods use reactive species that can damage dielectrics and/or mask resists, the cleaning methods avoid such damage by maintaining concentrations of the reactive species low during veil cleaning. Thus, the new cleaning methods do not cause incidental damage that would otherwise result if metal veils were removed with conventional cleaning solutions that are based on the same reactive species.
In one aspect, the invention features a method that includes performs a dry etch to produce one or more via holes in an upper layer of a structure. The dry etching stops on a metal layer that underlies the upper layer in the structure. The method includes cleaning the dry etched structure with an aqueous solution of hydrogen peroxide and either an ammonium salt or an amine salt.
In another aspect, the invention features an aqueous solution that includes hydrogen peroxide and either an ammonium salt or an amine salt. The aqueous the solution has a pH between about 4 and about 9.